Electrode construction



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InvehTor VicTor- J. Francis l6 ATTorn e3.

Patented Feb. I, 1949 UNITED 2,460,739 ELECTRODE ooNs'rnUcrroN Victor James Francis, Wembley, England, as-

signor to General Electric Company,'a corporation of New York Application February 25, 1947, Serial No. 730,808

In Great Britain April 17, 1946 Claims. (Cl. 17.6126) My invention relates to electrode constructions for electric discharge devices, and more particularly to electrode constructions for high pressure mercury vapor lamps of the kind which operate at a relatively high loading, that is, at a relatively high value of power in watts, as, for example, 100 or more watts. per cm. of arc length.

In high pressure lamps employed heretofore, it has been usual to use non-activated electrodes, that is to say. electrodes which are not activated upon those surfaces on which the electric discharge terminates in normal operation, hereinafter referred to as terminal surfaces. Activating material for starting purposes is commonly located away from said surfaces. When such lamps which operate satisfactorily on direct current, are operated on alternating current, hot spots often develop and are followed by tree growth," that is to say.metal of the electrode projects into the discharge space beyond the original terminal surface. The result of this is an unduly rapid vaporization of the electrode material and deposition thereof on the walls of the envelope with consequent reduction in useful life of the lamp. It is generally not practical to activate the ter minal surfaces in the usual Way because the activating material is rapidly vaporized. Various arrangements have been employed heretofore in electrode construction to provide activating material to the terminal surface during operation of the discharge device or the lamp in which the electrodes were used. However, many of these arrangements have been deficient for various rea- For a better understanding of my invention reference may be had to the following description taken in connection with the accom anyin drawing and its scope will be pointed out in the appended claims. Fig. 1 illustrates a high pressure mercury vapor lamp including electrodes constructed in accordance with my invention; Fi s. 2 and 3 are enlarged cross-sectional and end views respectively, of an electrode constructed in accordance with my invention; Figs. 4 and 5 illustrate a variation Of an electrode constructed in accordance with my invention.

end thereof.

Referring now more particularly to Fig. 1, m invention is there illustrated as applied to an electric discharge device of the high pressure typ such as a high pressure mercury vapor lamp of the short-gap type comprising a quartz envelope I and having positioned therein a plurality or pair of electrodes 2 and 3. Electrodes 2 and 3, where the lamp is intended for operation on alternating current are of similar construction, and each includes a terminal surface at the The distance between the electrodes 2 and 8, in this short-gap high pressure lamp, is less than the transverse inside'dimension of the envelope i at the portion of the envelope surrounding the arc discharge path. A quantity'of mercury is employed, as the ionizable medium, the quantity preferably being in sons, one of the most important of which has vapor lamps, and which comprises a solid body member or rod of refractory metal having at one end thereof a terminal surface in which there is a recess which contains activating material and an insert or plug held by the walls of the recess' but permitting the passage of activating material to the terminal or are supporting surface of the electrode during operation of the device or lamp in which the electrode is employed.

. The end of the solid body member and the plug constitute thereby the stated terminal surface which is a substantial portion of the cross-section-al area of that end of the body member.

constructed of a piece of solid refractory metal,

such as tungsten. providing at .the end thereof a terminal surface which supports an are discharge during normal and intended operation. A recess 4, which interrupts the smooth continuity of the body member end and which is preferably cylindrical in shape, is provided in or facing the terminal surface, and extends into the body part of the electrodes. Recess d, in the case of electrodes of- 4 millimeters in diameter, may be of the order of 1 millimeter in diameter and 4 millimeters in depth. ,A plug 5 of refractory metal, such as tungsten. is inserted in the recess and is constructed to have a shape similar to but slightly smallerthan that-of the recess 4 in order to provide an annular channel or space 6 which permits the passage of activating material 1 to the terminal surface from the pocket defined by the plug 5. and the bottom of the recess 4. The

tungsten plug 6 may extend about 2 millimeters into the recess 4 from the terminal surface. With electrodes of larger diameter the ratio of recess diameter to electrode diameter will usually be less than A. If desired, the recess may extend throughout the length ofthe electrode.

Insert or plug 5 is preferably cylindrical in shape and is constructed to provide relatively loose engagement with the wall of recess 4, thus permitting the plug 5 to remain in the position illustrated but allowing the activating material 1 to seep through the interstices established by the zone of engagement between plug 5 and the wall of the recess 4. The diamcterof plug 5 is chosen relative to the diameter of the recess sothat the plug 5 is maintained in the position shown, and at the same time permits the passage of the activating material'to the terminal suris obtained by connecting conductor 28 to the lead-in wire 12.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrode structure for an electric discharge device of the high pressure type, the combination comprising a cylindrical body member of tungsten having at one end thereof a terminal surface, a recess transverse to the longitudinal or slot transverse to the longitudinal axis of electrode 2. A plug or sintered mass of activating material I is placed in the slot and the open end of the trough or slot is provided with a refractory metal insert such as a tungsten insert or plug 0 which lies in and constitutes part of the terminal surface thereby shielding the activating material, and thus serving to protect the activating plug from direct effects of the are discharge. v

In either of the above-described variations, activating material for starting purposes may be provided away from the terminal surface in addition to that inset into the end of the electrode.

Returning now to Fig. 1, the electrodes 2 and 3 are fused and sealed to the envelope I by suitable seal constructions which may comprise strips 10 and H which are electrically connected to the body members of electrodes 2 and 3 and which are connected to lead-in wires Hand [3 having ends thereof externally accessible.

In order to minimize temperature diiferences appearing over the surface of the envelope I, I may employ an outer envelope l4 defining about the inner envelope I an evacuated space which serves to equalize the temperature distribution.

As a means for supporting the envelope I and the associated electrode structure in the position shown, I employ a suitable structure wherein the outer glass envelope l4 is preferably provided with a stem tube l5 and exhaust tube through which the envelope l4 may be exhausted. The

support for the lamp comprises a conductive support or frame 86, bent into a substantially U or rectangular-shaped frame having its upper ends sealed in a stem press [1. One end of the wire frame i6 is attached to an outer lead Wire H! which in turn is attached to a screw-threaded shell 19, having a skirted base 20. The other end of the supporting frame l3 terminates in the stem press II. The lower end of the frame is braced by a substantially semicircular and resilient wire 2! located at the bottom of the outer envelope IQ. Wire 2| is attached to the lower end of frame l6 by a wire member 22 which is welded at its middle to lead wire l3 and its ends to wire 2|. In this manner electrical connection to electrode 3 is established and to electrode 2 axis of said member in said terminal surface, activating material in said recess, and a. barshaped plug inserted in said recess for protecting said material from direct effect of the arc discharge and permitting activating material to pass to the terminal surface.

2. In an electrode structure for an electric discharge device of the high pressure type, the combination comprising a cylindrical bo y member of tungsten having at one end thereo a. terminal surface, a trough transverse to the longitudinal axis of said member in said terminal surface, activating material comprising thoria and zirconia in the form of a plug in said trough, and a bar-shaped plug inserted in said trough for protecting said material from direct effect of the arc discharge.

3. In an electrode structure for an electric discharge device of the high pressure type, the combination comprising a rod member of refractory metal, one end of said rod having a recess, activating material in said recess, and a plug in said recess, said end and plug defining a terminal surface constituting a substantial portion of the cross-sectional area of said end.

4. In an electrode structure for an electric dis\ charge device of the high pressure type, the combination comprising a solid cylindrical body member of tungsten, one end of said body member having a cylindrical recess, activating material in said recess, and a cylindrically-shaped plug in said recess for protecting said material from the direct effect of the arc discharge and permitting activating material to pass to the terminal surface, said-end and plug definin salt; terminal surface constituting a substantia portion of the cross-sectional area of said end.

5. In an electrode structure for an electrit dis-- ing 'substantiallyinto said recess for protectingsaid material from direct effect of the are discharge, said end and the last-mentioned plug defining a terminal surface constituting a substantial portion of the cross-sectional area of said end.

VICTOR JAMES FRANCIS.

REFERENCES CITED The following references are. of record in the file of this patent:

Davies Oct. 3], 1939 

